1. Field of the Invention
The present invention generally relates to a method for forming a mask, and more particularly, the present invention relates to the method for forming the mask being utilized for lithography processes in semiconductor device fabrication.
This application is a counterpart of Japanese application Serial Number 58822/2000, filed Mar. 3, 2000, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
In general, as high integration advance, exposing technique has changed from exposing technique in a lump to electron beam exposing.
FIG. 1 is a plane-view showing a photo-mask according to a conventional art.
As shown in FIG. 1, a first region 200 shown with a slanting line in a photo-mask is not exposed. Since an area of exposure pattern 202 per unit area in a left side region of a broken line L-Lxe2x80x2 is less than a half exposure area in the photo-mask, the exposure pattern 202 is defined as a small region. Since an area of exposure pattern 204 per unit area in a right side region of a broken line L-Lxe2x80x2 exceeds a half of all exposure area, the exposure pattern 204 is defined as a large region.
FIG. 2A-FIG. 2E are cross-sectional views showing a method for forming a mask using an electron beam exposure taken on line K-Kxe2x80x2 of FIG. 1.
As shown in FIG. 2A, a light-shielding layer 102 such as chrome is formed on a quartz substrate 100. Then a positive-type resist film 104a having a thickness of 300-500 xcexcm is formed on the light-shielding layer 102.
As shown in FIG. 2B, the resist film 104a is exposed using electron beam exposure. Here, dosage of the electron beam exposure is 6-10 [xcexcC/cm2]. Then, the exposed resist film 104a is developed. As a result, a resist pattern 104b is formed.
As shown in FIG. 2C, for removing resist remained on the light-shielding layer 102, a slight etching process is carried out.
As shown in FIG. 2D, the light-shielding layer 102 is etched using the remained resist pattern 104d as a mask.
As shown in FIG. 2E, the remained resist pattern 104d is removed. Processes as described above form photo-mask.
In processes as described above, as shown in FIG. 2A, when small and large regions of the exposure pattern 204 are formed depending on location of region, an opening size difference causes such as sizes A and B shown in FIG. 2B.
The opening size difference causes by fogging effect. The fogging effect has disclosed that xe2x80x9cShimomura, N., Ogasawara, M., Takamatsu. J., Yoshitake, S., Ooki, K., Nakayamada, N., Okabe, F., and Tojo, T.: xe2x80x9cReduction of fogging effect caused by scattered electrons in an electron beam systemxe2x80x9d, Part of the SPIE Symposium on Photomask and x-ray Mask Technology VI yokohama, Japan, September 1999, pp. 408-415xe2x80x9d.
Since an opening size difference such as sizes A and B exists, the resist pattern 104C if formed so that a size C of opening 107 is smaller than a size D of opening 108, as shown in FIG. 2C. Accordingly, as shown in FIG. 2E, an opening size F in the large region is formed larger than the designed size even if an opening size E in the small region is formed as designed.
It is desired to form opening size of the light-shielding layer 102 as designed without depending on the location of region formed resist pattern in the mask.
An object of the present invention is to provide a method for forming a photo-mask that can form an opening dimension of the light-shielding layer pattern as designed without depending on the location of region formed resist pattern in the photo-mask.
According to one aspect of the present invention, for achieving the above object, there is provided A method for forming a mask comprising: forming a light-shielding layer on a substrate; forming a resist film having small and large regions on the light-shielding layer, the small and the large regions being defined as the exposed area; exposing the resist film with low dosage using electron beam exposure according to a predetermined pattern data; and forming a resist pattern having a first opening in the small region and a second opening in the large region by developing the exposed resist pattern; wherein the elevation angle of the first opening sidewall in the small region is smaller than an elevation angle of the second opening sidewall in the large region.